Pulmonary limits of oxygen tolerance in man

As part of a comprehensive study of specific organ oxygen tolerance [1-4], oxygen effects on pulmonary function were measured in normal, resting men who breathed oxygen continuously at 3.0, 2.5, 2.0, and 1.5 atmospheres absolute (ATA) for average durations of 3.4, 5.7, 9.0, and 17.7 h, respectively. Rates of development of effects of pulmonary oxygen toxicity were monitored during oxygen exposure at 2.5, 2.0, and 1.5 ATA with repeated flow-volume loops, spirometry, and symptom assessment. Additional pulmonary measurements before and after exposure included lung compliance, airway resistance, density dependence of flow, nitrogen closing volumes, carbon monoxide diffusing capacity, and alveolar-arterial oxygen differences. Of these measurements only airway resistance and closing volumes were not significantly affected at any pressure, but patterns and magnitudes of effects varied at different pressures. Overall, the data indicate that continuous oxygen exposure at 3.0 to 1.5 ATA affects pulmonary mechanical function earlier and more prominently than CO diffusing capacity. Recovery of lung mechanical function usually occurred within 12-24 h after exposure, but required more than 24 h in some individuals. No individual measure of pulmonary function was found to be uniquely satisfactory for monitoring rates of development or reversal of pulmonary oxygen poisoning. The existence of multiple pulmonary effects of oxygen toxicity and the complexity of their interactions require selective applications of individual toxicity indices to specific conditions of exposure and recovery.